let num = 8
// number的判断
/*1. typeof number*/ 
console.log(typeof num == 'number');

/*2. Object.prototype.toString.call()*/
function isType() {
    let str = Object.prototype.toString.call(num)
    str = str.slice(8, -1)
    return str == 'Number' ? true : false
} 

/*3. !isNaN(parseFloat(value))*/
console.log(!isNaN(parseFloat(num))); 